This invention relates to control moment gyroscopic devices such as control moment gyroscopes (CMG) and reaction wheel assemblies (RWA).
CMGs and RWAs employ rapidly spinning rotors, powered by electric motors, that have a high cross-axis angular stiffness on the axis that is perpendicular to the spin axis. A low angular stiffness can significantly influence the weight, power, induce vibration (IV) and control requirements of the CMG or RWA. Following conventional teaching, CMG rotors are constructed with several components that are welded together, forming a stiff almost spherical structure. RWAs are a bit different: the rotor does not have as much cross-axis angular stiffness. Sometimes an RWA rotor is one piece, a rim connected to a shaft by a web.
A so-called multi-piece CMG rotor may contain five (5) pieces: a rim, which provides the bulk of rotating mass, and spherically contoured shell halves connecting the rim to a shaft. The components are connected using electron beam welding after some initial fabrication, followed by a final machining step. The manufacturing process is long and expensive. An RWA, having a simpler design because of less stringent structural requirements, is manufactured with less manufacturing steps, often in one piece.